Coal gasification process

ABSTRACT

A process for coal gasification whereby coal is converted to carbon monoxide, hydrogen and other gaseous products by contact with molten sodium sulfate, said sodium sulfate being reduced to sodium sulfide, which is regenerated with oxygen to sodium sulfate to provide a cyclic process.

01111 States atent 11 1 1111 3,770,390

Qhong Nov. 6,1973

[54] COAL GASIFICATION PROCESS 3,708,270 1/1973 Birk et al. 48/202 3,252,773 5/1966 Solomon et al..... 48/202 [75] lnvemor- Manuel Clmng, 3,236,589 2 1966 Reinhall et al 423/428 x 73 Assigneez Sun Research and Development Co, 3,252,774 5/1966 McMahon et al. 48/214 3,438,722 4/1969 Hercdy et a1. 423 242 Philadelphia, Pa.

[22] plied: 1971 Primary Examiner.loseph Scovronek [21] Appl. No.: 191,691 AttorneyGeorge L. Church et al.

- 52 0.5.01 48/202, 48/210, 252/373, 57 ABSTRACT 423/232, 423/648 51 Int. Cl. Cl0j 3/00, ClOj 3/46 A Process gasficam" whereby coal [58] T1610 64 Search 48/202 210 197 R- vetted Carbon monoxide, hydrogen. and other 423/415 8 eous products by contact with molten sodium sulfate, said sodium sulfate being reduced to sodium sulfide,

[56] References Cited which is regenerated with oxygen to sodium sulfate to UNITED STATES PATENTS Pmvide a cyclic, process" 3,567,412 3/1971 Lefrancois et al. 48/202 5 Claims, 2 Drawing Figures 1 K1 xwa w /2 M i a (afir/aw @4555 ans/r/cwflg/v 9 2M ZQYZQ EZ w 122 i -/Z /6 ,1, I I. n M1! M9215 E I ffl IVE; .5 7'0 QPf/OA/AL cweao/vflr/fl/v 1 cont GASHFICATHON PROCESS It is known in the art to effect gasification of coal by use of a molten sodium carbonate stream as a heat transfer medium (Report to the Office of Coal Research, PB 180,358, Sept. 1967). An advantage of such a process is that it produces a high BTU fuel gas from coal without requiring a separate oxygen plant. However, in the sodium carbonate process, the gasification reaction, which is shown by Equation 1,

u,o+c -+co+n (1) is endothermic and therefore some of the coal'being used in the process is burnedas fuel yielding nonrecoverable combustion products.

It has now been found, in accord with the process of this invention, that an improved coal gasification procedure results when coal particles are oxidized by means of molten sodium sulfate, said sodium sulfate being reduced to sodium sulfide which, in turn, is oxidized with an oxygen source to sodium sulfate for recycling to the coal gasification reaction. The process of the invention has numerous advantages, not the least of which is the exothermic nature of the reaction which results in essentially all of the coal being converted to product gas. In addition, the process of the invention requires minimum gas flow and this permits low capital investment for equipment, thus yielding a more economical process. Furthermore, the process of the invention employs sulfates and sulfides in the reaction equipment which results in less attack on the oxide refractories used as linings than experienced herefore with carbonate systems.

The cyclic oxidation reduction system used in the process of the invention is exemplified by the following Equations 2 and 3:

Na SO 4c Na s 4C0 (2) N s Na S0,

The overall reaction of the process of the invention is thus illustrated by Equation 4:

troduced at line ill to the coal gasification reactor 12,

which contains molten sodium sulfate at a temperature of about 950C to about l,l00C. Reaction of the coal with the sodium sulfate occurs to yield gasification products such as carbon monoxide, hydrogen, hydrogen sulfide, etc. which exit from the reactor at line 13. it is desirable to introduce an amount of coal which will maintain an excess of carbonaceous material in gasifying vessel 12 in order to minimize over reaction of hy drogen to H 0 and C0 to CO which can occur from side reactions. The inclusion of water vapor with the coal introduced at line 11 is desirable for a hydrogen rich product in that it increases the ratio of hydrogen to carbon monoxide in the product gases by reaction (1) above. Theamount of water vapor used will generally not exceed'about 50 parts per 100 parts of coal. The sodium sulfide produced in the process together with some unreacted coal proceeds from the reactor through line 14- to oxidizer 15,-an internal screen or other barrier 12a preventing an excessive amount of solid coal particles from being carried into oxidizer 115 with the molten sulfide. Air or other source of oxygen, which may first be taken through a preheater 17, is introduced at line 16 to the oxidizer 15, where the sodium sulfide is oxidized to sodium sulfate and unreacted carbon is converted to carbon dioxide. This latter gaseous product together with nitrogen is taken off through line 18 and through heat-exchanger 17 where sensible heat may be recovered in the usual manner. The sodium sulfate formed in the oxidizer is returned through line 19 to the coal gasification reactor 12,

where it is, of course, used for conversion of additional coal to gaseous products. If it is desired to have a sulfur scrubbing system in the process so as to reduce or eliminate sulfur products in the off gases, this is readily done by adding Na CO to the system, which reacts with sulfur compounds to form sodium-sulfur salts:

c ms Na CO M s 200 (5) 40 so na co, Na S sco (6) Sodium carbonate may readily be regenerated by taking a drag stream of the sodium sulfide 20 and treating it with CO and H 0:

co m0 Na S Na CO ms (1) The H 8 may then be converted to elemental sulfur or other useful products. A drag stream 2% will also be useful to prevent build up of coal ash even if the optional carbonate scrubbing system is not used. lt will be understood that the amount of Na co used will depend upon the sulfur content of the coal feed, but, in general, about 5 percent by weight Na C0 in the molten salt phase will be adequate for desulfurization. The exact level of Na CO to be used is readily determined by experiment.

A preferred method of operating the circulation systern for the process is illustrated in H6. 2. As illustrated here, particulate 'coal is introduced to the gasification reactor 22 through line 2E and the gaseous products of the reaction are taken off at line 23. The molten sodium sulfide-in reactor 22 flows by means of gravity through line 24 to the bottom of the oxidizer vessel 25,

and the carbon dioxide and nitrogen gases generated here are taken off through line 26. The sodium sulfate in the oxidizer 25 flows by gravity through line 28 to the bottom of the gasification vessel 22, where it is again able to react with coal introduced into the system. This gravity flow circulation system is aided by the gases generated which lift the materials to the top of each vessel and since there is a significant difference in density between the materials in the lines as compared to the aerated materials in the vessels, there is a flow pattern-generated as described above. Although it is to be expected that some aeration will occur in the lines,

especially in line 28 where coke can react with Na SO to form CO, this gas formation will not be enough to inhibit flow, since line 28 will be relatively cold compared to the bottom of the gasification vessel 25, where major reaction of coal with sulfate occurs. No pumping equipment need be used in this circulating system and this makes for an economical and efficient process.

ln a typical procedure, for each parts by weight of coal (on a moisture free, ash free, and S N, and 0 free basis) and 4.8 parts of steam introduced to the coal gasification reactor at l,O00C and atmospheric pressure and 36.7 parts of 20' to 25C air fed through a heat exchanger to the oxidizer which is at about l,l00 to 1,200"C temperature and atmospheric pressure, the products formed will be 22.4 parts by weight of CO and 0.9 parts hydrogen from the gasification reactor and 28.2 parts of nitrogen issuing from the oxidizer. It will also be understood that the gasification products may be subjected to the gas shift reaction to produce hydrogen and this is readily accomplished by water quenching the gases to provide evaporative cooling at the same time as providing part of the water needed for the reaction: C0 H O C0,, H For a-required shift reactor feed temperature at 400C with the gaseous products indicated above coming out of the gasifier at about 1,050C, about 8.5 parts of liquid water will be injected to accomplish the cooling needed and about 5.9 parts additional water will be used for the shift reaction.

The invention claimed is:

l. A process for .coal gasification which comprises feeding particulate coal to a gasification reactor containing molten sodium sulfate at a temperature of from about 950C to about 1,100C, removing gaseous products from said reactor, conducting molten sodium sulfide produced in said reactor by reaction of said sulfate with said coal by gravity flow from the upper portion of said reactor to a bottom portion of an oxidizer vessel which is fed with oxygen and in which oxidizer vessel said sulfide is oxidized to sulfate at a temperature of about l,l00 to about 1,200C, conducting said molten sodium sulfate by gravity flow from the top of said oxidizer vessel to the bottom of said gasification vessel for further reaction with coal.

2. A process as in'claim l where coal and water vapor are fed to said molten sodium sulfate.

3. A process as in claim 1 where sulfur compounds from the coal are removed from the system by maintaining in said molten sodium sulfate about 5 percent by weight of sodium carbonate to react with said sulfur compounds.

4. A process for coal gasification which comprises feeding particulate coal and water vapor to a gasification reactor containing a mixture of molten sodium sulfate and sodium carbonate at a temperature of from about 950C to about l,l00C, removing gaseous products from said reactor, conducting molten sodium sulfide produced in said reactor by reaction of said sulfate with said coal and by carbonate with sulfur compounds by gravity flow from the upper portion of said reactor to a bottom portion of an oxidizer vessel which is fed with oxygen andin which oxidizer .vessel said sulfide is oxidized to sulfate at a temperature of about l,100C to about 1,200C, conducting said mixture of molten sodium sulfate and sodium carbonate by gravity flow from the top of said oxidizer vessel to the bottom of said gasification vessel for further reaction with coal.

5. The process of claim 4 where said sodium carbonate is regenerated by treating a drag stream of the sodium sulfide with CO, and H 0. 

2. A process as in claim 1 where coal and water vapor are fed to said molten sodium sulfate.
 3. A process as in claim 1 where sulfur compounds from the coal are removed from the system by maintaining in said molten sodium sulfate about 5 percent by weight of sodium carbonate to react with said sulfur compounds.
 4. A process for coal gasification which comprises feeding particulate coal and water vapor to a gasification reactor containing a mixture of molten sodium sulfate and sodium carbonate at a temperature of from about 950*C to about 1,100*C, removing gaseous products from said reactor, conducting molten sodium sulfide produced in said reactor by reaction of said sulfate with said coal and by carbonate with sulfur compounds by gravity flow from the upper portion of said reactor to a bottom portion of an oxidizer vessel which is fed with oxygen and in which oxidizer vessel said sulfide is oxidized to sulfate at a temperature of about 1,100*C to about 1,200*C, conducting said mixture of molten sodium sulfate and sodium carbonate by gravity flow from the top of said oxidizer vessel to the bottom of said gasification vessel for further reaction with coal.
 5. The process of claim 4 where said sodium carbonate is regenerated by treating a drag stream of the sodium sulfide with CO2 and H2O. 